This invention concerns a laminated resin material using a fiber reinforced thermoplastic resin made by a dispersion method as a substrate material which is suitable, for example, to automotive interior materials. Particularly, it relates to a laminated resin material in which the fiber reinforced thermoplastic resin is expansion molded and a skin material is adhered.
In recent years, weight-reduction in automobiles has been progressed and a demand for the reduction of weight to automotive interior materials has also been increased.
Referring to an example of a headliner material as one of automotive interior materials, fiber reinforced thermoplastic resins made by a dispersion method in which inorganic fibers such as glass fibers are fixed as a core material thereof with a thermoplastic resin such as polyethylene or polypropylene have been used predominantly. This is because it has a merit capable of compatibilizing the weight reduction and the strength. As the fiber reinforced thermoplastic resin made by the dispersion method, it has been known that an expansion moldable stampable sheet is suitable.
The stampable sheet is produced by a dry dispersion method or a wet dispersion method. The stampable sheet by the dry dispersion method is formed by dispersing discontinuous reinforcing fibers and thermoplastic resin fibers or particles in a gas phase to form a non-woven fabric-like precipitates (webs), and then heating and pressuring them to solidify into a sheet-form. This is disclosed, for example, in JP-A-2-169632. On the other hand, the stampable sheet by the wet dispersion method is formed by dispersing discontinuous reinforcing fibers and thermoplastic resin fibers or particles in a liquid medium such as water or bubbles, making non-woven fabric-like precipitates (webs) from liquid dispersion and then heating and pressurizing them to solidify into a sheet-form. This is disclosed, for example, in JP-B-55-9119 or JP-A-60-58227.
The stampable sheet can be shaped easily by heating to a temperature higher than the melting point of the thermoplastic resin as a matrix. In the stampable sheet, reinforcing fibers are opened to monofilament state and piled. Accordingly, when the thermoplastic resin of the matrix is melted, it tends to resume the state of webs before solidification owing to the rigidity of the reinforcing fibers or the like to recover the thickness near the thickness of the web. A molding product with an increased thickness can be obtained utilizing the nature described above by placing a thermally expanded stampable sheet in a die, compressing the same while adjusting a clearance of the die such that voids are left after solidification and cooling in the molding product and then cooling and solidifying the product. Such a molding method is referred to as expansion molding which is shown, for example, in JP-A-4-331138. The obtained molding product (hereinafter also referred to as an expanded molding product) has a three dimensional network structure in which reinforcing fibers are dispersed in random directions and entangled. This is a porous body in which crosslinked reinforcing fibers are secured with the thermoplastic resin.
Along with development of such expansion molding products, with a view point of providing further weight reduction and high rigidity, the expansion molding products have been utilized recently, for example, as the core material for automotive interior materials. For example, a laminated product obtained by disposing an adhesive layer on one side of a stampable sheet, laminating a skin material such as a non-woven fabric on the adhesive layer in a state of thermally expanding the stampable sheet, compressing the same to a desired thickness, bonding the stampable sheet with the skin material, integrating and then expansion molding the same (hereinafter also referred to as an expansion molded laminated-product) has been utilized as automotive headliner materials. As apparent from the example of the application use described above, the automotive interior material using the stampable sheet is required to have not only high rigidity but also high adhesion strength between the stampable sheet and the skin material. For obtaining high rigidity, there is a method of expansion molding the stampable sheet to increase the thickness of the interior material. That is, since the rigidity is in proportion with the cube of the thickness, upon expansion molding of the stampable sheet (the compression ratio is decreased) when a clearance is increased, the thickness of the interior material is increased to enhance the rigidity.
However, in a case of increasing the clearance during molding for enhancing the rigidity, since the compression ratio is small, the adhesion pressure is also decreased, so that the adhesion strength between the stampable sheet and the skin material can not always be said sufficient. On the other hand, when the clearance during molding is decreased (compression ratio is increased), the adhesion strength naturally increases but high rigidity can no more be obtained since the thickness of the interior material is decreased. As described above, the rigidity and the adhesion of the skin material are contrary to each other and it is difficult to obtain an expansion molded laminated-product capable of sufficiently satisfying both of them.
In a case of adhering a skin material by way of an adhesive resin to a porous material such as an expansion molded stampable sheet, a thermoplastic resin is preferably used for the adhesive resin. It has been known so far that the adhesion with the skin material is improved, that is, adhesion strength is increased more by the use, for example, of low density polyethylene with lower melt viscosity as the adhesive resin. As more concrete examples, there are proposed a thermoplastic resin film having a melt flow rate (hereinafter may be simply referred sometimes also as MFR) of 0.5 g/10 min or more (JP-A-7-9632), a polyethylenic resin having MFR of 5.0 to 30.0 g/10 min (JP-A-7-68721), a thermoplastic resin film having MFR of 3 g/10 min or more (JP-A-8-164562), a linear low density polyethylene having MFR of 3 g/10 min or more (JP-A-2000-15729) and the like. A resin having a higher MFR has higher fluidity and lower melt viscosity.
However, when the present inventors have examined adhesion between the expansion molded stampable sheet and the skin material by using a low density polyethylene having an MFR of 15 g/10 min as the adhesive resin, satisfactory adhesion strength could not always be obtained. It should be noted that the adhesive resin used belongs to a thermoplastic resin having an MFR of 0.5 g/10 min or more as proposed in JP-A-7-9632 described above.
Then, the present inventors have made earnest study on the cause described above and, as a result, have found that reduction of the melt viscosity of the adhesive resin at a low shear rate (for example, shear rate: 10 sxe2x88x921) is important for increasing the adhesion strength with the skin material while increasing the thickness of the expansion molded laminated-product as it is (low compression ratio during molding), and have accomplished this invention.
Generally, the melt viscosity of thermoplastic resin has a shear rate dependency as shown in FIG. 1. That is, under the constant condition for the temperature, the melt viscosity is higher when the shear rate is lower, whereas the melt viscosity is lower in a case where the shear rate is higher. Any of MFR proposed in the prior art described above is a measured value in a high shear rate region usually of 2000 to 10000 sxe2x88x921 of shear rate.
However, the shear rate dependency on the melt viscosity of the thermoplastic resin differs variously depending, for example, on the kind and the molecular weight of the resin. For example, even when the melt viscosity in the high shear rate region is relatively lower compared with the melt viscosity of other resins, the melt viscosity in the low shear rate region is not always lowered to a same extent. As schematically shown in FIG. 1, the melt viscosity between the resins may sometimes be reversed depending on the case. The present inventors have found that the adhesive strength relative to the skin material can be increased by the use of a thermoplastic resin having a lower melt viscosity in the low shear rate region. It has been found that the rigidity can be maintained as it is and, in addition, the adhesion strength with the skin material is also improved while maintaining high rigidity by the use of such an adhesive resin, even when the thickness of the expansion molded laminated-product is increased.
An object of this invention is to provide a laminated resin material excellent in the adhesion with a skin material, having high rigidity and reduced in the weight, as well as a precursor thereof.
This invention provides a laminated resin material comprising: (1) a fiber reinforced thermoplastic resin layer made by a dispersion method, (2) a gas impermeable resin layer on the fiber reinforced thermoplastic resin layer, and (3) an adhesive resin layer having a melt viscosity of not more than 5000 Pa.s under a shear rate of 10 sxe2x88x921 at 150xc2x0 C. and not more than 250 Pa.s under a shear rate of 2000 sxe2x88x921 at 150xc2x0 C. on the gas impermeable resin layer.
In the laminated resin material, the fiber reinforced thermoplastic resin layer made by the dispersion method described above is preferably one of members selected from the group consisting of stampable sheets and webs thereof.
Further, any of the laminated resin layers preferably includes those in which the fiber reinforced thermoplastic resin layer made by the dispersion method is an expansion molded stampable sheet, and which further has a skin material on the adhesive resin layer.